The Flashman Papers by George MacDonald Fraser and their existence present an interesting scenario as there aren't too many changes compared to OTL. The differences would be mainly academic and debates about his character and life (such as whether he was exaggerating his exploits).
- The existence of a state called the Duchy of Strackenz in Schleswig-Holstein and its annexation to Germany in 1848 might be the only major difference. Fraser's publication of Flashman's memoirs about this in 1970 might arouse some separatist feelings (or a desire to join Denmark) in the former duchy once the inhabitants find out what Bismarck and his henchmen were doing in Strackenz. There would also be a scandal over Flashman's suggestion that Rudi von Starnberg was the father of Duchess Irma's son.
- The 1842 retreat from Kabul might not be remembered in Britain as much of a defeat as it is in OTL given Flashman survived and 'led' the defence of Piper's Fort. After the publication of the first packet of papers, I imagine there will be a lot of revisionism about the retreat, siege, and Flashman's role. Sergeant Hudson would probably be given a posthumous award or statue as Flashman admitted in his memoirs that he (Flashman) stole all of the credit for the defence of Piper's Fort.
- As Flashman and the Tiger states, Sherlock Holmes and Dr Watson exist in this universe with all of their own adventures. I'd expect a few historians to look at Tiger Jack Moran (Colonel Moran) more sympathetically based upon what happened to him in Flashman and the Tiger and Flash for Freedom.
- One of the 'introductions' to the books has Fraser receive a letter from an American man who claimed to be a grandson of Flashman after the latter's encounter with a woman in New Orleans. Flashman himself hints that there is a descendant of his in Russia who is the son of a Russian noblewoman. Though, it's questionable whether this Russian Flashman's descendants would have survived the Soviet purges. Presumably, there would be many other claims of Flashman heritage as he was very lecherous. Whole Flashman societies could form based around his descendants.
- Flashman himself would go through various phases of historical reception. The books imply he falls into historical obscurity in the early 20th century. Fraser's publication of Flashman's memoirs apparently revive considerable interest in him. As he was involved in many of the major conflicts of the Victorian era, there would be a sort of 'Flashmania' for a time. It would take the form of historical debate about Flashman's life and whether he was really dishonourable. By the early 21st century, I can see Flashman fading again due to his racism and misogyny. If Flashman's American Civil War memoirs are published after Fraser's death, they might be censored to remove all of the racist language. He also might lose a few statues and street names in the aftermath of the 2020 George Floyd protests.